This research is aimed at understanding the regulation of gene expression in animal cells with specific emphasis on transcription and processing the primary nuclear transcripts (hnRNA) into messenger RNA (mRNA) HnRNA contains a large number of oligo U sequences that are conserved in a significant fraction (15-20%) of the polyadenylated mRNA's of the cytoplasm. The structure of these mRNA's, their translatability and sequence relationships to mRNA's lacking oligo U's are being studied. Nuclear polyadenylated RNA also contain branched structures formed by a phosphodiester bond at the 3 feet hydroxyl group of a nucleoside that is already linked via the normal 3 feet 5 feet phosphodiester bond to an adjacent nucleotide. The absence of branched structures from polyadenylated mRNA leads us to suspect such structures are involved in a nuclear RNA processing reaction. Structural analysis and localization and distribution of branches in RNA sub-populations are proposed. Branches will be sought in adenovirus primary transcripts to develop a well-defined system for studying the possible role of branches in nuclear RNA processing.